Flameless Chemical Heaters (FCH), also known as Flameless Ration Heaters (FRH), are used in Meal, Ready-to-Eat (MRE) packaging to provide hot meals to soldiers in the field or for warming or heating medical supplies or food rations in confined spaces (e.g., tents, underwater shelters) or in remote locations where there is no heat source. These FCHs or FRHs are generally based on the reaction of magnesium with water to form magnesium hydroxide and hydrogen which releases about 85 kcal of energy per mole of magnesium. Equation [1] below sets forth this reaction.Mg+2H2O→Mg(OH)2+H2+Δ  [1]
There are two types of MREs. The first is an individual meal for the soldier. The second one is a family-style meal for a group of 10-20 soldiers, called the Unitized Group Ration-Express (UGR-E). Both of these MREs use a Flameless Ration Heater (FRH) as the heat source for the hot meal. The temperature of a 250 gram individual MRE entrée can be raised by 100° F. in about 10 minutes using a 14 g FRH. Typically, the process of heating food consists of adding about 40 ml of water to the FRH by the military or other user, in order to activate the chemical reaction that produces the heat. Presently, the FRH consists of a magnesium, iron and salt mixture. The iron is used to activate the reaction of magnesium with water, whereas the salt prevents the formation of a magnesium oxide film on the magnesium metal surface. The reaction products are magnesium hydroxide and hydrogen. With the individual MRE, the liberation of up to 13 liters of hydrogen gas has not been a substantial safety problem.
The Unitized Group Ration-Express (UGR-E) is a complete meal in a box and can feed small groups of eighteen soldiers. Again, the food is heated by using a proportionally larger FRH that is activated by the addition or distribution of water. The problem associated with the release of hydrogen is significantly magnified with group meals. For a UGR-E weighing 28 pounds and requiring approximately 400 g of heater material, the amount of hydrogen released is typically 13.5 cubic feet or 380 liters. Thus, the concern is that generation of this large quantity of hydrogen in a confined space will exceed the Lower Explosive Limit of 4%.
Accordingly, there is a need for an improved system for the elimination, or at least minimization of hydrogen generation in magnesium/water based flameless heaters.